Bipolar mercury cathode cell with mercury splitter

ABSTRACT

A mercury splitter for breaking an electrical current in a mercury cell circuit having a plurality of vertically stacked monopolar or bipolar cell units. The mercury splitter has a compact arrangement of individual splitter units. Each splitter unit includes an upper tray and a lower tray. The upper tray divides the mercury into fine streams which free fall, dividing into drops. The lower tray collects the mercury, forming a stream that is electrically separate from the mercury in the upper tray.

United States Patent [72] Inventors Carl W. Raetrsch;

John F. Van Boozer; Hugh Cunningham, all of Corpus Christi, Tex.

[21] ApplQNo. 865,467

[22] Filed Oct. 10, 1969 [45] Patented Oct. 26, 1971 [73] Assignee PPG Industries, Inc.

Pittsburgh, Pa.

[54] BIPOLAR MERCURY CATHODE CELL WITH MERCURY SPLITTER 7 Claims, 8 Drawing Figs. [52] US. Cl 204/219, 204/220, 204/250, 204/275, 74/8 [51] Int. Cl C22d 1/04, BOlk 3/00 [50] Field of Search 204/219, 220, 250, 275; 74/8 [56] References Cited UNITED STATES PATENTS 2,673,232 3/1954 Silsby, Jr. 204/275 X 2,700,650 1/1955 Denora 204/219 2,719,117 9/1955 Blue et al 204/220 3,398,080 8/1968 Steffanson et al. 204/2l9 3,400,055 9/ 1968 Messner 204/220 X 3,499,829 3/1970 Messner et al 204/2 1 9 FOREIGN PATENTS 91,479 2/1958 Norway 204/220 Primary Examiner]ohn H. Mack Assistant Examiner-D. R. Valentine Attorney-Chisholm and Spencer ABSTRACT: A mercury splitter for breaking an electrical current in a mercury cell circuit having a plurality of vertically stacked monopolar or bipolar cell units. The mercury splitter has a compact arrangement of individual splitter units. Each splitter unit includes an upper tray and a lower tray. The upper tray divides the mercury into fine streams which free fall, dividing into drops. The lower tray collects the mercury, forming a stream that is electrically separate from the mercury in the upper tray.

PAIENTEnncize ISTI 3.616.431

sum 2 OF 4 INVENTORS F a 2 CARL W- BAETZscH JoHM F. m Hpozm Hum CUNN/A/fiHAM BY M 8 ATTOR NEYS BIPOLAR MERCURY CATHODE CELL WITH MERCURY SPLITTER This invention relates to the electrolytic production of alkali metal hydroxides using a cell of the type having a flowing mercury cathode The invention relates, more particularly, to a method and apparatus for breaking the electrical current in the mercury circuit at a point or points between the electrolytic cell and the denuder unit.

One of the principal methods of producing alkali metal hydroxides from alkali metal halides is by alkali metal chloride electrolysis in a mercury cathode cell. Such cells, typically, comprise a long, relatively narrow trough and an anode which is suspended above and spaced from the trough. The anode is usually made of graphite or a platinum group metal, the latter including ruthenium, rhodium, palladium, osmium, iridium, and platinum, as well as alloys and oxides of such metals on a suitable corrosion-resistant substrate. The cathode is comprised of a stream of mercury that enters the cell at one end, flows along the trough, and leaves the cell at the other end. The alkali metal halide or, in other words brine, enters the cell at the one end, flows through the cell in the space provided between the anode and the flowing mercury cathode. The halidc, generally chloride, ions in the brine are attracted to the anode during cell operation and discharged as gas. The cation, generally sodium, forms an amalgam with the mercury. The depleted brine is fortified after leaving the cell, for example, with solid sodium chloride. The fortified brine is then recircu lated through the cell. One highly desirable bipolar mercury cathode cell is disclosed in U.S. application Ser. No. 410,579, now abandoned which is assigned to the assignee of the present invention.

The amalgam, after leaving the cell, is treated in a denuder where the sodium reacts with water to form sodium hydroxide, hydrogen gas, and regenerated mercury. The regenerated mercury is again sent to the cell. In such a cell arrangement, a separate dcnuder is provided for each and every electrolytic cc For various obvious reasons, it would be desirable to have a single denuder which would treat amalgam from a plurality of cells, the foremost reason being economics. Mercury is an ex cellent conductor of electricity and, therefore, if the plurality of mercury output streams from different cells or cell units are fed directly into a single denuder, shorting between the cells will occur. in addition, there would be current loss due to grounding.

Means have previously been proposed for breaking the electric current in a mercury stream. For example, U.S. Pat. No. 3,400,055 discloses feeding the mercury stream to a wheel having a plurality of electrically insulated compartments. The wheel rotates and carries away electrically isolated segments of the mercury stream. Another somewhat similar means for breaking electrical current in a mercury stream is disclosed in U.S. Pat. No. 938,191 where a ceramic wheel is provided with a plurality of pockets. As the wheel rotates, the pockets dip into a mercury pool. When the individual pocket reaches its uppermost position. the mercury is relessedinto a trough. Although these circuit breakers permit feeding a plurality of mercury streams to a single denuder, they are not completely satisfactory. For example, they have moving parts and thus require maintenance as well as consuming power during operation. Moreover, such structures are complex and provide a limited amount of electrical resistance.

The present invention is an improvement on the invention disclosed in commonly assigned patent application Ser. No. 809,486 and provides apparatus for breaking the electrical current in a mercury stream in a very simple manner without the use of moving parts or the consumption of power. Furthermore, the present invention provides a very high and constant electrical resistance. for example, above 100,000 ohms and, on occasion, as high as 3,000,000 ohms or higher, compared with conventional wheel-type electrical circuit breakers which provide a fluctuating resistance ranging as low as about 100 ohms. The present invention provides means for breaking up the mercury stream into'smsll drops. The small drops are separated by an air space, thereby providing excellent electrical isolation. The mercury splitter disclosed in patent application Ser. No. 809,486 provides an excellent electrical break in the mercury stream; however, using that splitter it is necessary to provide a separate mercury splitter for each cell unit. The present invention provides a single mercury splitter having a plurality of splitter units and is capable of handling a plurality of mercury streams. Thus using the present invention one needs only one input mercury splitter and one output mercury splitter for a mercury cathode cell including a plurality of cell units.

The splitter of the present invention can be used in other environments where an electrical break is needed in a mercury stream, As used herein with respect to the splitter, the term mercury will include elemental mercury, the amalgam of the particular alkali metal such as sodium, potassium, lithium, ru bidium, or cesium, as well as a mercury'amalgam mixture.

In the drawings:

FIG. 1 shows a bipolar mercury cell arrangement including mercury splitters of the present invention.

FIG. 2 is a vertical, cross-sectional view of the input mcrcury splitter of the present invention.

FIG. 3 is a horizontal, cross-sectional view taken along the line llIIll in FIG. 2.

FIG. 4 is a horizontal, cross-sectional view taken along the line IV-JV in FIG. 2.

FIG. 5 is a vertical, cross-sectional view of the output mercury splitter of the present invention.

FIG. 6 is a view taken along line VI VI in FIG. 5.

FIG. 7 is a view taken along line VIl -VII in FIG. 5.

FIG. 8 is a view taken along line VIII-VIII in FIG. 5.

The bipolar cell arrangement illustrated schematically in FIG. 1 utilizes the present invention for breaking an electrical current in a mercury circuit or, in other words. electrically isolating the individual cell units. The bipolar cell 10 includes 3 cell units; namely cell units 11, 12, and 13. Each of the cell units has an anode and opposed mercury cathode, the cathode being in direct electrical contact with the anode of the next a lower unit, thus connecting the cell units in a series arrangement. The bipolar cell 10 also includes an input mercury splitter 17 and an output mercury splitter 18. A mercury stream is fed to the input mercury splitter 17 by a feed line 21. The splitter 17 electrically separates the mercury stream and sends the mercury to each of the cell units 11, 12, and 13. An output line 22 carries the combined mercury-amalgam mixturn from the cell units in cell 10 to the denuder 23. The output mercury splitter 18 provides an electrical break between the mercury streams leaving the individual cell units 11, 12, and 13 and the common mercury stream carried by output line 22.

The mercury input or feed splitter 17 (FIG. 2) includes a container 30 which is preferably cylindrically shaped; how ever, it could be otherwise, such as rcctangularly shaped, without departing from the present invention. The container 30 has a cylindrical sidewall 31, a bottom wall or plate 32, and atop wall or plate 33. Sidcwall 31 has an outwardly extending flange 34 near the upper edge thereof. The top wall 33 is removably secured to flange 34 by bolts 36 and 37. A gasket or seal 38 may be provided between the top wall 33 and flange 34 of sidewall 31. The bottom wall or plate 32 is secured to sidewall 31 such as by welding.

The mercury feed splitter 17 further includes a splitter feed pipe 41 which is connected to feed line 21 and which feeds mercury to a plurality of splitter units 42, 43 and 44. The splitter teed pipe 41 extends through the container 30 and'is located in the center thereof or, in other words, is concentric therewith. The pipe 41 enters container 30 through opening 46 in the bottom plate 32 and leaves the container 30 through opening 46 in the bottom plate 32 and leaves the container 30 through opening 47 in top plate 33. The feed pipe 41 has a radially extending flange 48 secured thereto such as by welding. Feed pipe 41 is attached to bottom plate 32 by bolts 49 and 50 which extend through suitable openings in flange 48 and bottom plate 32. A gasket or seal 51 is provided between flange 48 and bottom plate 32. Mercury is preferably fed into the lower end of pipe 41. The upper end of pipe 41 may be used as an overflow, thereby maintaining a substantially constant head of mercury.

The feed pipe 41 has a plurality of nozzles 55, 56, and 57 for feeding mercury to the splitter units 42, 43, and 44, respectively. The nozzles each have orifices which control the amount of mercury delivered to the corresponding mercury splitter unit. Preferably, the nozzles are of an adjustable type so that the amount of mercury being delivered to the splitter unit can be controlled as desired.

The mercury splitter units 42, 43, and 44 may be identically constructed; therefore, only unit 42 will be described. Mercury splitter unit 42 is comprised of an upper tray 61 and a lower tray 62. Lower tray 62 and the cell unit feed pipe 77 are electrically isolated from the remainder of the splitter unit by use of suitable electrically insulating materials or by fabricating the parts from electrically nonconductive materials, for example from plastic materials such as polyvinyl dichloride, KYNAR, TEFLON or fiberglass-reinforced polyester or epoxy resins. The trays 61 and 62 may be secured to and supported by the splitter feed pipe 41, for example, by welding when weldable plastic materials are used. As shown in FIGS. 3 and 4, the trays 61 and 62 may be arcuate in shape. The upper tray 6 includes a bottom plate 63 and sidewalls 64, 65, 66, and 67. The plate 63 has a plurality of small openings 68 therein through which mercury may pass, thereby being divided into small streams. The openings may be circular in cross section and, preferably, have a diameter of between one thirty-second inch and five thirty-second inch. The tray 62 is substantially the same size and shape as tray 61, is vertically aligned with tray 61, and is electrically insulated from feed pipe 41 and other trays of the unit.

The tray 62 is spaced downwardly from the tray 61 a sufficient distance to permit the falling mercury to divide into drops and, preferably, the mercury should continue to free fall at least 1 inch after dividing into discrete drops. The tray 62 will rarely be spaced less than 4 inches or more than 24 inches from tray 61. Usually, tray 62 will be spaced between 8 inches and 12 inches from tray 61. The lower tray 62 has a solid bottom plate 71 and sidewalls 72, 73, 74, and 15. A cell unit feed pipe 77 extends from tray 62 of splitter unit 42 to cell unit 11. The pipe 77 carries mercury from the splitter unit 42 to the cell unit 11. As shown in FIGS. 2, 3, and 4, the mercury splitter units 42, 43, and 44 are circumferentially ofi'set from each other, thereby permitting the splitter units to overlap one another providing a highly compact structure. For example, the uppennost splitter unit 42 is circumferentially offset from mercury splitter unit 43 and the lower tray 62 of the uppermost splitter unit 42 is located lower in container 30 than is the upper tray 61A of the next lower splitter unit 43.

The mercury exit splitter 18 (FIGS. 5-7) is constructed somewhat similar to the mercury splitter 17. Mercury splitter 18 is comprised of container 80 and the splitter column 81. The container 80 includes cylindrical-shaped sidewall 82, a top wall or lid 83, and a receptacle 84. The splitter column 81 is supported in the container 80 and is concentric with sidewall 82. The splitter column 81 includes a pipe 87 containing a helical flight 90 supported on a central shaft 89. The helical flight 90 has a diameter substantially the same as pipe 87. The lower end of pipe 87 has openings 91 through which mercury may pass.

A plurality of splitter units such as splitter units 92, 93, and 94 are supported on the pipe 87 radially outwardly thereof. The splitter units 92, 93, and 94 are substantially identical; therefore, only splitter unit 92 will be described herein. The splitter unit 92 includes a feed pipe 96 which carries the mercury exit stream from the mercury cell units to the splitter 18. Feed pipe 96 and splitter unit 92 are electrically isolated from the remainder of splitter unit 18. The splitter unit 92 further includes an upper tray 97 and a lower tray 98. The trays 97 and 98 may be secured to pipe 87, such as by welding. The

upper tray 97, which is electrically isolated from the unit, includes a perforated plate 99 and sidewalls 100, 101, and 102. The plate 99 has a plurality of openings 103 therein for purposes hereinafter described. The lower tray 98 is likewise supported by pipe 87 and may be welded thereto. The lower tray 98 includes a solid plate 106 and sidewalls 107, 108, and 109. An opening 111 is provided in pipe 87 adjacent the lower tray 98. The opening 11 is for removing mercury from tray 98. The receptacle 84 (FIGS. 5 and 8) includes a pair of sidewalls 113 and 114, and end wall 115, and an arcuit end wall 116. The end wall 116 is the lower portion of sidewall 82 of container 80. The recepticle 84 further includes a bottom wall 117 and a lid or cover 118. The recepticle 84 also includes a dam 121 which extends thereacross and is secured to the sidewalls 113 and 114 such as by welding. A passage 122 is provided in the bottom wall 117 so that the mercury which is collected behind dam 121 may pass beneath the dam and out of the discharge splitter 18 through the pipe 123. The outlet pipe 123 is connected to line 22 which extends to a denuder as shown in FIG. 1.

When the bipolar cell 10 is in operation, a mercury stream is fed to splitter 17 by the pipes 21 and 41. Portions of the mercury stream pass through each of the splitter units 42-44. For example, one portion of the mercury stream passes through nozzle 55 into tray 61 of splitter unit 42. Further portions of the mercury stream pass through the nozzles 56 and 57 into the splitter units 43 and 44, respectively. The mercury passes through openings 68 in tray 61, thereby being divided into small streams. As the fine streams of mercury free fall, they break up into separate drops or spheres, resulting in an electrical break in the mercury stream. The mercury is then collected, preferably in a pool in the lower tray 62 or on the mercury-Wettcd surface of the plate 71 of tray 62 and is removed through the pipe 77 which leads to the mercury cell unit 11. By forming the drops during uninterrupted free falling (contrasted with other means of breaking up mercury, e.g., by impinging the streams against a solid surface), the drops are assured of being of a substantially uniform size and of a maximum size, preferably a diameter of between one thirtyseconds and five thirty-seconds inch in horizontal cross section. In such state, the droplets unite with facility into a single body in tray 62, whereas impinging a mercury stream against a surface produces drops of various sizes, many of which are too small to be easily collected and reunited but rather tend to produce a foam. Furthermore, the falling drops of the present invention preferably should be prevented from impinging against a hard surface such as plate 71 with sufficient force to fracture the drops into droplets that are too small to be easily reunited. The mercury streams from the splitter units 42, 43, and 44 then pass through the mercury cell units 11, 12, and 13, respectively, where the brine is electrolyzed and a mercury-alkali metal amalgam is formed. The mercury and amalgam mixture then passes to the respective splitter units 92, 93, and 94 of the output splitter 18. The mercury-amalgam mixture, for example, from unit 11, is fed to the splitter unit 92 by way of feed pipe 96. The mercury-amalgam mixture passes through openings 103 in tray 97, thereby being divided into fine streams which free fall to the lower tray 98. As the streams free fall, they form into discrete droplets, thereby providing an electrical break in the mercury stream. The drops are then collected in the lower tray 98 and passed through opening 11 in pipe 87 and run down the helical flight through openings 91 to the receptacle 84. The mercury passes from the receptacle 84 through the outlet pipe 123 and line 22 to the denuder 23 where the alkali metal amalgam is converted into the alkali metal hydroxide and elemental mercury. In the described splitter units it is understood that electrical isolation of the divided mercury or mercury-amalgam streams is necessary to accomplish the desired purpose. While KYNAR, polyvinyl dichloride, TEFLON and fiber-glass-reinforced polyester and epoxy resins have been mentioned as materials of construction, other methods of construction employing suitably insulated metals, rubber-lined metals, and

electrically nonconducting plastic materials are equally acceptable.

Although the present invention has been described with reference to the specific details of particular embodiments thereof, it is not intended thereby to limit the scope of the invention except insofar as the specific details are recited in the appended claims.

We claim:

I. In a bipolar mercury cathode cell for producing alkali metal hydroxides by the electrolysis of an alkali metal halide brine, said cell including a plurality of cell units, a common mercury feed line communicating with each of said cell units for feeding mercury to the cell units, a common mercuryamalgam output line communicating with each of said cell units'for receiving mercury-amalgam mixture from the cell units, and a denuder communicating with said output line for receiving and treating said mercury-amalgam mixture, the improvement comprising:

] a mercury splitter disposed between said cell units and the feed line and a mercury splitter disposed between said cell units and the output line, at least one of said mercury splitters comprising:

frame means and a plurality of mercury splitter units supported by said frame means, each of said splitter units comprising mercury supply means including distributor means for dividing the mercury into small streams and collecting means spaced downwardly from said distributor means, said distributor means and collecting means being electrically insulated from each other, said space being unobstructed and of sufficient length to permit the small streams to free fall until the streams divide into discrete drops, thereby electrically isolating the mercury supply means from the mercury-collecting means, said mercury splitter units being arranged about a common axis circumferentially ofiset from one another and axially overlapping one another.

2. The bipolar mercury cathode cell as defined in claim I wherein said frame means comprises a vertically disposed pipe, said mercury splitter units being supported by said pipe.

3. The bipolar mercury cathode cell as defined in claim 2 wherein said mercury splitter units are arcuately shaped.

4. The bipolar mercury cathode cell as defined in claim 2 wherein each of said mercury splitter units comprise:

a first tray including sidewall means and bottom wall means, said bottom wall means having defined therein a plurality of fine openings through which mercury may pass thereby providing fine streams of mercury;

a second tray spaced downwardly from said first tray, said second tray including sidewall means and bottom wall means whereby the mercury that falls from said first tray is collected in said second tray.

5. The bipolar mercury cathode cell as defined in claim 4 wherein said fine openings have a diameter of between one thirty-second and five thirty-seconds inch.

6. The bipolar cell as defined in claim 2 wherein said pipe is a mercury splitter input line which supplies mercury to each of the splitter units.

7. The bipolar cell as defined in claim 2 wherein said pipe is a mercury splitter output line and includes a helical flight means down which the mercury may flow.

i t 0 i 

2. The bipolar mercury cathode cell as defined in claim 1 wherein said frame means comprises a vertically disposed pipe, said mercury splitter units being supported by said pipe.
 3. The bipolar mercury cathode cell as defined in claim 2 wherein said mercury splitter units are arcuately shaped.
 4. The bipolar mercury cathode cell as defined in claim 2 wherein each of said mercury splitter units comprise: a first tray including sidewall means and bottom wall means, said bottom wall means having defined therein a plurality of fine openings through which mercury may pass thereby providing fine streams of mercury; a second tray spaced downwardly from said first tray, said second tray including sidewall means and bottom wall means whereby the mercury that falls from said first tray is collected in said second tray.
 5. The bipolar mercury cathode cell as defined in claim 4 wherein said fine openings have a diameter of between one thirty-second and five thirty-seconds inch.
 6. The bipolar cell as defined in claim 2 wherein said pipe is a mercury splitter input line which supplies mercury to each of the splitter units.
 7. The bipolar cell as defined in claim 2 wherein said pipe is a mercury splitter output line and includes a helical flight means down which the mercury may flow. 